Description: (Applicant s Description) The overall objectives of this project are (1) to develop a chemoprevention method for prostate cancer and (2) to develop a practical approach for testing prostate cancer chemoprevention efficacy in clinical trials. The applicant proposes as general approach to first test the ability of chemopreventive agents reduce prostate-specific antigen (PSA) levels in men with rising PSA as the first sign of Recurrent prostate cancer following radical prostatectomy in a double-blind, randomized trial. Subsequently, the investigator will test in a double-blind, randomized trial the ability of the agent(s) that is/are active in this respect to delay prostate recurrence following radical prostatectomy (as measured by PSA failure using an ultra sensitive PSA assay) in men that are at high risk for this. In parallel, he will also determine whether these agents reduce the frequency of occurrence and/or quantity of circulating prostate cancer cells, as measured by a highly sensitive RT-PCR method that detects mRNA for prostate-specific membrane antigen (PSM) produced by these cells; this is a potential marker for the risk of progression to metastatic prostate cancer. Soy protein and dehydroepiandrosterone (DHEA) have been selected as the two agents that will be tested in this project for their cancer chemoprevention efficacy. If substantive effects in the desired direction are found in the proposed studies, the stage is set for future prevention clinical trials in men at high risk for developing clinically evident prostate cancer.